Patent Literature 1 discloses a technique of determining a different vehicle that encounters a host vehicle by using information acquired from the different vehicle via inter-vehicle communication. The technique of Patent Literature 1 matches, on a map, a position of the host vehicle acquired from a car navigation apparatus and a position of the different vehicle acquired from the different vehicle via the inter-vehicle communication. Then, the nearest intersection ahead of the host vehicle is extracted from a map database (hereinafter, DB) based on the position of the host vehicle on the map, and a series of intersections on a travel road where the different vehicle continues traveling straight is extracted from the map DB based on the position of the different vehicle on the map. When the series of intersections on the travel road of the different vehicle includes the nearest intersection ahead of the host vehicle and when the different vehicle enters the nearest intersection ahead of the host vehicle in a different direction from the host vehicle, the different vehicle is determined to encounter the host vehicle.